I recently tested my 9 month old aquaponics out of curiosity. To my surprise my Phosphorus was off the chart dark purple high. I have read that this may contribute to fish illness out of toxicity. I don't remember the source. I do have a dark algae in half of my tank trying to take over so I decided to lower my Phosphorus to a safer level. After four days of using Seachem PhosGuard my level dropped in half. Now I'm gonna remove the Seachem PhosGuard since I noticed my nitrates have dropped. It seems like a good product to use temporarily.

Unless u have a problem with your fish I would leave it alone. Phosphorous is good for the plants. No need to add phosphorous either. Just add fish food and iron. Rarely there can be potassium issues, but most likely it's a PH problem.

I add small amounts of mono-potassium phosphate (MPK) if it looks like phosphates are running low. It's slightly acidic so I also add some hydrated lime. For example, 1 tsp (5 ml) of MPK will result in about a 5ppm increase in phosphates in my 1000 L system. Along with the 1 tsp of MPK, I add only a pinch of hydrated lime to offset the acid.

At low levels, in addition to being good for plants and harmless to fish, phosphate is an effective pH buffer.

The man was asking you all! about what he could use to safely dose phosphates with in his system and all you did is babble on about how you don't need it and leave it alone or test for it. if you don't know how to explain to him what he needs then don't bother posting. Your wasting your time and everyone that reads your post.

Yes in ap systems that have fruiting plants you MUST keep your P level at min around 20 - 40 for cannabis is closer to 80. NOW that being said why doesn't someone with a bit more understand of what can be used to add phosphates to your ap system preferably to the fish tank its self chime in because some of us like to know these things!

Hmm, I think there are a couple of comments that might help, although, they won't give you your dosing thawee .

In most systems the phosphorus comes from the fish food but gets bound very quickly especially above pH 7 (there is usually quite a bit of excess phosphorus in fish food), it may or may not be available to the plants or detectable by testing with the API kit or any other method (like all tests, what you detect depends on how you process the sample and how it's bound to other compounds). You can usually tell if a system is running detectable phosphorus levels because there is lots of algae growth. If there were adequate plants to take up the phosphorus in the grow beds, the algae wouldn't be there. If it were bound in the solids in the grow bed, again, the algae wouldn't be there because there wouldn't be dissolved phosphorus available - at least this is my belief and I admit I could be wrong.

thawee wrote:

Yes in ap systems that have fruiting plants you MUST keep your P level at min around 20 - 40 for cannabis is closer to 80.

I think beliefs like this come from the world of hydroponics and in relation to how AP behaves, I don't believe this. Have you noticed how many people run systems with zero nitrates, yet the plants still grow. All it means to have low or no phosphorus levels is that the plants are using all the detectable phosphorus as it is produced or that it's all being bound and has become undetectable. In a Hydro system you'd add all the nutrients at once and you can't let the levels fall below a certain amount but it's not getting bound in complex organic compounds. In AP where you are adding extra phosphorus through the fish food on a daily basis and where you often can't detect what's there because it's bound, it's possible and not really unlikely to run low levels by testing but still have good flowering. Hope this makes sense.

i can speak for myself only but in the case of my response to juno81, i tried to stear him away from adding phosphorous specifically because the information he provided about his problem did not sound ;like phosphorus deficiency so i was giving him advice that might save him time and money.

If you are focusing on plants that [actually] have a P demand then a lot can come down to system design.*If* you have a few fish (particularly fish for food where you desire growth) and you feed a lot then yes - mostly P and K is going to be OK. But in some systems that may not be the case - eg. some goldfish systems where the growth rates may not make lots of feeding cost-beneficial. I experience this issue for example with tomatoes. The cost of fish food far exceeds B&B etc.

I get around it by using media based dutch buckets (20-25L bucket or square drum type are good) - these allow me to use things like small amounts of dynamic lifter and blood & bone with added potash. The buckets can be set up to not flush as aggressively as a grow bed and this helps keep the nutrients local - and you find lots of worms. These types of products are organic and breakdown can be assisted by gentle watering can application of system water every now and again or else rain will do it.

*But* it is not necessary to target P or K levels specifically in AP as one does for as one would N or one would in a hydroponics system. (as many of the original posters eluded to). As many posts note in AP you don't really want too much P circulating as it sets off algae.

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